As a miner, your goal in life is to collect enough diamonds to unlock the exit to the next level, all the while happily digging through levels with some impassable walls and... boulders of course! Lots of them.
Boulders obey the laws of gravity, and as such will happily fall onto your head lest you be vigilant not to trigger their fall, or fast enough to dodge them.
Later on, monsters also roam the underground corridors and give you a chance to further refine your skills at last-second boulder dodging - you let the monsters get the hit on the head!

This particular installment of the game boasts 24x4 levels of digging fun.

Here is a full hack for the game Boulder Dash where all the levels are changed as well as the sprites.

Boulder Dash (USA).nes - NOINTRO
CRC32: 008F1536
MD5: DCE99ECF42F72FCBB09487B2E5390073
SHA-1: 45220F3A088E154A9531E8E2B17583AD5E9B35D6
SHA-256: 86BB5B51A9962DBE94B6B92658A28EDFAD8EA6D3E19E2787C956DD759D931073